<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=<device-width>, initial-scale=1.0">
    <title>Document</title>
    <style>
        div {
            /*外边框*/
            margin: 50px;
            /*margin-left: 20px*/
            /*边框*/
            border: 5px solid blue;
            /*内边框*/
            padding: 50px 10px;
            /*padding-centre: 10px*/
            background-color: greenyellow;
            height: 100px;
            width: 100px;
        }
    </style>
</head>
<body>
<div>
    我是内容
</div>
<p>我是p标签</p>

</body>
</html>